1. Field of the Invention
The present invention relates to a thin-film magnetic head for magnetic recording including an electromagnetic coil element having a magnetic layer with a non-magnetic layer therewithin, a head gimbal assembly (HGA) provided with the thin-film magnetic head, and a magnetic disk drive apparatus provided with the HGA.
2. Description of the Related Art
With the increasing demand for small, and yet high-capacity magnetic disk drive apparatus in recent years, further improvements in recording density have become essential. One of the important factors for increasing recording density is an improvement in write characteristics of thin-film magnetic heads in the high-frequency band of data signal, which includes the maintenance or improvement of the write field intensity.
Generally, an electromagnetic coil element for writing data signals of the thin-film magnetic head has, in the case that the head is for longitudinal magnetic recording, a lower magnetic layer (a magnetic layer on the leading side) and an upper magnetic layer (a magnetic layer on the trailing side) that sandwich a write gap layer. These magnetic layers act as magnetic poles. In such a head, the improvement of the write characteristics in the high-frequency band requires eddy-current loss generated in the magnetic layers to be suppressed, as well as requires an adequate soft-magnetic material to constitute the magnetic layers. The eddy-current loss increases as data signals have higher frequency, and causes the write characteristics to be degraded by disturbing the response of the magnetization of the magnetic layers to the signal field.
A technique for suppressing the eddy-current loss is disclosed, for example, in Japanese Patent Publication 08-102013A, in which the portion of an upper core and/or lower core other than the portion overlapping with a front intermediate core has a multilayered structure in which a non-magnetic insulating layer is sandwiched between magnetic layers. The non-magnetic insulating layer is intended to decrease the eddy-current loss, and further, to realize a flat frequency characteristic because the non-magnetic insulating layer is not formed in the portion overlapping with the front intermediate core and is not exposed from the opposed-to-medium surface, and therefore does not contribute to the formation of pseudo-gap.
Further, Japanese Patent Publication 11-25419A discloses a thin-film magnetic head having an upper core in which a first magnetic film, non-magnetic insulating film and a second magnetic film are sequentially stacked. In the head, the thickness of the non-magnetic insulating film is set to be less than 50 nm (nanometers) and to be one tenth of the magnetic gap or less so as to suppress eddy-current loss and further magnetic flux leakage due to the interposition of the non-magnetic insulating film.
However, even using the above-described conventional techniques utilizing the non-magnetic insulating layer (film) within the core in a certain form, there has been a problem that sufficient write characteristics in the high-frequency band is difficult to be obtained. That is to say, there has been a problem of the difficulty in obtaining sufficient write field intensity, of the occurrence of adjacent track erase (ATE), of the increase in thermal pole tip protrusion (TPTP) due to write currents, and further of the increase in non-linear transition shift (NLTS).
Actually, in the thin-film magnetic head described in Japanese Patent Publication 08-102013A, the non-magnetic insulating layer exists in the portion other than the portion overlapping with the front intermediate core, and therefore, reaches the end on the side opposite to the opposed-to-medium surface of the upper core and/or lower core. As a result, a magnetic flux leaks out from the end, which reduces the intensity of the essential write field in the write gap position.
Also, the technique described in Japanese Patent Publication 11-25419A has the same problem, in which the non-magnetic insulating layer can reach the end on the opposed-to-medium surface side, as well as the end on the side opposite to the opposed-to-medium surface. In the technique, the thickness of the non-magnetic insulating layer is adjusted to deal with this magnetic flux leakage problem, however, the case may occur that such thin-film magnetic heads cannot sufficiently corresponds to further miniaturization and higher frequency of data signals.
Moreover, the technique requires that the saturation magnetic flux density of the first magnetic film is set higher than that of the second magnetic flux density, which restricts the design of the magnetic circuit.
In addition, suppressing the ATE, suppressing the TPTP due to write currents and reducing the NLTS, as well as improving the write field intensity, are important points to solve the problem of the write characteristics in the high-frequency band.
Here, the ATE is a phenomenon in which unwanted write or erase operation is performed to the adjacent track on the magnetic disk as a magnetic recording medium due to the increased influence of the leakage field from a magnetic pole, under the condition that the width in the track width direction of the magnetic pole becomes smaller according to higher frequency of data signals. The TPTP due to write currents is a phenomenon in which the end of the magnetic head element is protruded toward the surface of the magnetic disk due to such as Joule heat from the coil layer and heat of eddy-current loss in the magnetic poles and shields (magnetic layers), both of which are generated by applying write currents to the coil layer. When the end of the magnetic head element has a contact with the surface of the magnetic disk due to the TPTP, the frictional heat by the contact causes the electric resistance of a magnetoresistive (MR) effect element for reading data signals to be changed, so that a problem (thermal asperity) such as the occurrence of abnormal signals is likely to occur, and further, the probability of crash becomes high.
The NLTS is a shift in time of read signals, which is caused by the shift in the position of the magnetization reverse in the record bit during writing, generated by the influence of the magnetization of existing record bits. The increase in the NLTS has a possibility to bring a negative effect to the demodulation of data signals.
However, the above-described conventional techniques just utilizing the non-magnetic insulating layer (film) within the core have had no consideration for suppressing/reducing these phenomena.